Teeth whiteners, also known as teeth bleaching agents, are in widespread use as a cosmetic means to enhance appearance and, generally, to contribute to better oral health and hygiene.
Particularly popular and most effective among these devices are those whose chemistry is based on peroxides, of which hydrogen peroxide and carbamide peroxide (representing an adduct of hydrogen peroxide and urea) are most frequently employed. Such peroxides are characterized by their lack of stability resulting in the generation of radical (atomic) oxygen, the chemical action of which is responsible for the desired whitening/bleaching effect. The generation of atomic oxygen is, however, highly undesirable during storage of such peroxide-based teeth whitening devices. Thus, in their commercial form, such devices are formulated in a manner which attempts to inhibit premature peroxide decomposition. Contact with certain foreign objects, especially materials having highly developed surface areas; certain chemicals; and elevated pH accelerate the decomposition process of said peroxides and the liberation of radical oxygen.
Stability of such formulations, however, is in direct conflict with the purpose and object of their applications, namely achieving the best possible whitening effect in the shortest possible time of contact with the tooth surface. Consequently, teeth whitening devices of prior art formulations typically require multiple applications stretching over a period of weeks and even months, with each recommended application time usually being from two to eight hours.
Of the two forms of peroxides commonly used in commercial teeth whiteners, hydrogen peroxide is preferred for its faster action, while carbamide peroxide based formulations offer advantages in terms of greater storage stability, more desirable consistencies and handling properties, and less risk of damage to soft tissues. Stability of both hydrogen peroxide and carbamide peroxide-based formulations is greater, especially in the case of the former, at low pH, preferably in the range of 3-4.5. Carbamide peroxide based materials may, however, exhibit adequate stability even at neutral or near neutral pH. This makes such formulations more desirable from the standpoint of better perceived compatibility with mucosa and of having no or negligible detrimental effect on tooth enamel and on the health of teeth that are in less than intact condition.
Carbamide peroxide formulations are particularly stable in environments containing little or no water. Examples of carriers for carbamide peroxide most common to commercial use are glycerin and propylene glycol. While these carriers are considered nontoxic and convenient for their compatibility with desirable additives such as thickening agents, preservatives, flavors and therapeutics, their use may create some unwelcome, though generally minor, side effects. The most common side effect is discomfort caused by the desiccating effect of anhydrous (or nearly anhydrous) hydrophilic solvents/carriers on mucosa, especially pronounced when scarified or inflamed tissue is involved. Similar responses may also be expected in cases of leaching restorations or recessed gums.
Attempts have been made to accelerate the teeth beaching processes without increasing the concentration of the peroxide by using heat-generating devices, such as high intensity light emitting instruments or lasers. Because of the cost of necessary equipment and greatly increased risk of tissue damage associated with these techniques, they are designed for use exclusively by a dentist. Such treatments are necessarily expensive. The most effective of these techniques are those using lasers, but they also carry the highest possibility of inflicting damage on the teeth and/or soft tissue. The cost of treatments is considerably higher than when conventional methods are used.